I run two kvm guests on my host, with the same config. One of them is a ubuntu 17.10, the other is a debian 9.2. Both are running on linux kernel 4.13 (debian is installed from the backports repo) On the host side I see, Ubuntu's qemu process consumes nearly no cpu, while debian's uses 25%. On virt-manager's screen on the ubuntu's performance page I see 1-2% cpu usage, but 13% on debian's while they are in idle state.
If I logon to guest and run "top", then I see the system is in idle state. Have you got any idea, why consumes debian's qemu process so much cpu on the host? What can it do while the guest do nothing?